The invention relates generally to conveyors and, more particularly, to a conveyor capable of transporting food product through a freezer in a helical path.
The use of helical or spiral conveyors for carrying food product through freezers enables acceptable dwell time to be maintained in conjunction with acceptable product throughput rates, with efficient use of space. U.S. Pat. No. 3,315,492 discloses a freezer employing such a helical conveyor, wherein the tiers of the conveyor are supported by horizontal arms which extend into the stack. It has been recognized that compactness of freezers of this type may be improved by increasing the number of tiers without increasing the vertical dimension of the freezer, by making the belt self-supporting, which enables the horizontal arms to be eliminated, thereby permitting closer spacing of adjacent tiers while maintaining desired clearance for product. U.S. Pat. No. 3,938,651 discloses a conveyor arrangement wherein the belt is arranged in a self-supporting stack and the stack is supported on a second conveyor which is driven to rotate the stack. However, provision of a satisfactory conveyor for supporting the stack has proven to be problematic, and it has been found that a helical belt stack manufactured in accordance with the teachings of this patent are susceptible to collapsing under certain conditions.
U.S. Pat. No. 4,565,282 states as one of its objects to eliminate the disadvantages of prior art installations such as that of Pat. No. 3,938,651, which have not been able to carry the pile or stack through a continuous complete revolution due to the ingoing or outgoing lower part of the conveyor belt. The installation of U.S. Pat. No. 4,565,282 comprises two endless chains which are arranged under the belt pile so as to carry the belt through a complete revolution. However, the arrangement of Pat. No. 4,565,282 is complicated and expensive and is believed to be susceptible to problems due to ice formation interfering with proper functioning of rolling elements in the apparatus. U.S. Pat. No. 4,899,871 discloses an arrangement which is intended to address the problem of ice formation obstructing ball movement by employing a chain comprising overlapping links which are intended to exclude ice from the path of rolling elements. This proposed arrangement further increases the number of moving parts and adds to the expense and complexity of the apparatus.